With its technology tests almost complete, NASA's Deep
Space 1 mission is about to undertake the closest encounter with
an asteroid ever attempted when it flies within 15 kilometers (10
miles) of the newly named asteroid Braille tonight at 9:46 p.m.
Pacific time (July 29 at 04:46 Universal Time).

Deep Space 1 will rely on its experimental autonomous
navigation system, called AutoNav, to guide the spacecraft past
the mysterious space rock at a relative speed of nearly 56,000
kilometers per hour (35,000 mph).

"Deep Space 1's main purpose is to test advanced
technologies for the benefit of future missions, so we view the
flyby and its science return as a bonus," said Dr. Marc Rayman,
Deep Space 1's chief mission engineer and deputy mission manager
at NASA's Jet Propulsion Laboratory, Pasadena, CA, where the
mission is managed. "This ambitious encounter is a high-risk
endeavor, and its success is by no means guaranteed. But should
there be significant data return, the findings will be of great
interest to the science community."

This morning, the spacecraft experienced a "safing" event at
about 1200 UTC (5 a.m. PDT), during which Deep Space 1's flight
computer rebooted itself and the spacecraft halted activity to
wait for commands from Earth. However, the mission team and
spacecraft recovered quickly from the event, which is not
expected to impact tonight's flyby significantly. The spacecraft
is operating as expected.

Asteroid Braille was previously known as 1992 KD. The new
name was announced on Monday, July 26, by the Planetary Society,
Pasadena, CA, as the result of a contest that focused on inventor
themes and drew more than 500 entries from around the world. The
name honors Louis Braille (1809-1852), the blind French educator who
developed the system of printing and writing named for him and
used extensively by the blind.

The winning entry was submitted by Kerry Babcock of
Port Orange, FL. Eleanor Helin, who co-discovered the asteroid
with fellow astronomer Kenneth Lawrence, made the final decision
on the name. Helin and Lawrence are astronomers at NASA's Jet
Propulsion Laboratory (JPL), Pasadena, CA, which also manages
Deep Space 1.

During the encounter, Deep Space 1 will be in the
ecliptic plane (the plane in which Earth and most other planets
orbit the Sun), moving more slowly than the asteroid, which will
be progressing up through the ecliptic plane from below. It may
well be more appropriate to say that the asteroid will zoom by
Deep Space 1 than the reverse.

The flyby will allow final testing of AutoNav, which
enables the spacecraft to use images of distant stars and
asteroids within our Solar System to keep track of its location
in space and to guide trajectory changes. Deep Space 1 has successfully
completed tests of its 11 other new technologies.

The asteroid and the space environment surrounding it
make scientifically interesting targets for two advanced science
instruments aboard Deep Space 1. During the flyby, a
spectrometer and imaging instrument will send back black-and-
white photographs and images taken in infrared light, while a
second instrument observes the three-dimensional distribution of
ions and electrons, or plasma, in the area.

In addition to their value for designing future
missions, the images and other data returned from this encounter
will greatly assist scientists in understanding the fundamental
properties of asteroids. Although scientists believe Braille's
diameter is approximately 1 to 5 kilometers (0.6 to 3 miles),
they know little else about it. With this flyby, they can learn
more about its shape, size, surface composition, mineralogy and
terrain.

Launched on Oct. 24, 1998, from Cape Canaveral Air
Station, FL, Deep Space 1 marked the first launch of NASA's New
Millennium Program, which tests and validates new technologies
for future space and Earth-observing missions. The technologies
that have been tested on Deep Space 1 will help make future
science spacecraft smaller, less expensive and capable of more
independent decision-making so that they rely less on ground
controllers.

The mission has exceeded almost all of its technology
validation requirements by conducting more extensive tests than
had been planned. As one dramatic example, the spacecraft's
experimental xenon ion engine, which was required to thrust for a
minimum of 200 hours, has been operated for nearly 1,800 hours.

Deep Space 1 is budgeted at $152 million, including
design, development, launch and operations. The mission is
managed for NASA's Office of Space Science by JPL, a division of
the California Institute of Technology.